vm4

Virtual Machines

Two virtual machines that (almost) implements the same vm. One in C, and the other in Python3.

vm4

There is a sample.p that has been compiled to sample.b previously. You can run this on either of the virtual machines. First running the C variant:

> ./c.sh

And then the Python3 variant:

> ./py.sh

As (probably) can be observed, Python is roughly 50 times slower than C.

Sample

The sample is the factorial:

procedure factorial[n];
	var m, o;
	begin
		if n = 1 then return 1;
		o is n - 1;
		call factorial[o];
		return (n * rval)
	end;

begin
	call factorial[10];
	print rval
end.

Which translates into assembly:

C0002:
	LDARG 0
	ST 0
	LD 0
	SET 1
	EQ
	JPZ :L0003
	SET 1
	STORE 0
	RET
L0003:
	LD 0
	SET 1
	SUB
	ST 3
	LD 3
	STARG 0
	CALL :C0002
	LD 0
	LOAD 0
	MUL
	STORE 0
	RET
	RET
START:
	SET 10
	STARG 0
	CALL :C0002
	LOAD 0
	PRINT
	HALT

And then the assembler spits out the "binary" (integer) file:

38,13,0,28,0,12,0,27,1,5,11,16,27,1,30,
0,24,12,0,27,1,31,28,3,12,3,29,0,2,0,12,
0,14,0,18,30,0,24,24,27,10,29,0,2,0,14,
0,22,8

Which both machines can handle.

problems with different machines

Besides this sample above, it is easy to find samples that simply do not work on both machines. It depends upon implementations rather than some abstractions. But instead of defining our own specification, next we will look at a well known programming language, and the fact it already has a virtual machine: the Java Virtual Machine Specification.